Put very simply, hydrodemolition uses high pressure water to remove surface concrete down to the underlying metal support structure, or rebar as it is known in the construction trade
Before hydro demolition was established as a credible alternative, the favoured technique for stripping surface concrete was to use pneumatic jackhammers or hand chiselling in some sensitive areas. This highly destructive technique has now become outdated as it removes both good and bad concrete. It also causes damage to the remaining healthy, sound, concrete and the steel reinforcement, as well as injuring jackhammer operators.
In summary, the reasons you should not use destructive pneumatic methods to remove damaged surface concrete are:
About Hydro demolition
Undertaking hydro-demolition is not an easy, or simple job, but it can be extremely effective in terms of the end result and a very cost effective solution besides.
There are two main types:
Conventional Hydro demolition has traditionally involved an operator holding a lance.
Hydro-demolition uses twenty litres of water per minute at a pressure of 2500 bar pushing 25 – 30kg of reaction force on the human body. This means this approach can be dangerous and, much like the pneumatic jackhammer approach, also monotonous and hard physical work.
This means that, due to the physical requirements, an operator can sometimes only stand 10 or 15 minutes without having a break or rest. As the workday progresses operators become fatigued and because of this there is the potential for accidents to happen.
Conventional hydrodemolition therefore can, and should, only be used for small short spell jobs.
For larger jobs, Robotic Hydrodemolition is used as a more effective and safer solution.
Hydro demolition is a fast and efficient method of concrete removal, without damaging the surrounding structure and embedded rebar, utilising the power of high-pressure water.
A jet of high-pressure water is directed at the surface of the concrete where it penetrates the voids and micro-cracks. When the water pressure inside the voids overcomes the pressure of the concrete a small “blast” occurs and this breaks the concrete away.
Damaged concrete is usually weaker than good concrete and so, with the right settings, it is possible to obtain selective removal. This means that all the damaged and weak concrete is removed and the sound concrete is left behind.
The hydro-demolition robot ensures that the concrete surface is exposed to the water-jet systematically. The required removal depth will therefore not have to be specified accurately since the robot “measures” and removes the concrete at the same time.
Work rates of 0.3 – 0.4 m3 per hour can be expected when using a robot – a substantial increase on manual methods especially for sensitive areas where hand chisels may have to be used otherwise.
Operators are remote from the work being carried out and so suffer neither the physical stress of manual means nor run the risk of being injured by flying debris as the robot work head is completely shrouded.
As it is programmable, the robot’s work can be easily replicated. This means the same depth of cut can be executed within a predictable time frame on a given area of concrete. Project management is therefore improved as timescales can be more accurately calculated.
Potentially costly personnel training and maintenance requirements for robotic hydro demolition can be circumvented by subcontracting the work to specialists who hire out both the equipment and the operators. Whilst the headline cost of this can sometimes look expensive, a full evaluation of the package will usually reveal savings overall that can be substantial.
The industry trend is towards hydrodemolition and the Concrete Repair Association has offered guidance that states: “wherever possible hydro demolition should be the preferred method of concrete removal”.
There has also been a legislative change which is outlined in The Control of Vibration at Work Regulations 2005 (the Vibration Regulations).
The introduction of hydrodemolition techniques for the removal of defective concrete therefore complies with both legislative requirements and recommended industrial best practice.